Question

Tìm X

1+2+3+4+...+X = 210

Answer 1

x = 20 nha !

k mik nhé

Answer 2

\(1+2+3+4+...+x=210\)

Ta có : \(\frac{\left(1+x\right).x}{2}=210\)

\(\Leftrightarrow\left(1+x\right).x=210.2\)

\(\Leftrightarrow\left(1+x\right).x=420\)

\(\Leftrightarrow\left(1+x\right).x=21.20\)

\(\Rightarrow x=20\)

Answer 3

Ta có:1+2+3+...+x=[x.(x+1)] : 2=2010

=>x.(x+1)=2010.2

=>x.(x+1)=420=20.21

=>x=20

Ủng hộ mik nhé!

Answer 4

x = 20 nha bạn

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Answer 5

Ta có :

\(\frac{\left(x+1\right)x}{2}=210\)

\(\Leftrightarrow\left(x+1\right)x=420\)

\(\Leftrightarrow21.20=420\)

Vậy x = 20

                  Đ/S : ...